1. Field of the Invention
The invention relates to electric machines, and more particularly, it relates to rectifier electric drives incorporated in numerically or digitally controlled actuating mechanisms for various applications.
2. Description of the Prior Art
High reliability of synchronous machines and flexibility of their control have opened up broad horizons for their use in high-precision rectifier drives of automation devices which are currently widely employed in various technologies.
However, the hitherto known rectifier electric drives are devoid of means for compensating for pulsation of the driving torque caused by fluctuations of the supply voltage, varying impedance of the supply circuits, the finiteness of the impedance of real-life voltage sources, and reversal of the rotation of the drive. This narrows down the speed control range and steps up pulsation of the speed. Moreover, the flatness of mechanical characteristics is affected, which complicates the control of the position and speed of a synchronous machine.
There is known a rectifier electric drive (SU, A, 1144201) comprising a synchronous machine with a shaft position transmitter, a permanent or fixed storage having its address inputs connected with the outputs of a control unit and its corresponding outputs connected with the inputs of comparison circuits or comparators equal in number to the number of the windings of the synchronous machine. The outputs of the comparators are connected with a switching device connecting the windings of the synchronous machine to a voltage source. However, in this system the range of angular speed control is limited because of variations of the torque at reversing, the absence of means for compensating for pulsation and drift of the supply voltage, and the varying frequency of pulse-width modulation of the voltage across the windings of the synchronous machine. Furthermore, because of the finiteness of the impedance of the voltage source in a real-life electric drive, the flatness of this system's mechanical characteristics is not adequately high.
The above shortcomings are partly eliminated in a rectifier electric drive (SU, A, 1244779) comprising a synchronous machine provided with a shaft position transmitter having its output electrically connected with an address input of a permanent storage having recorded therein the code of duration and polarity of supply pulses fed to the windings of the synchronous machine, the output bus of the storage being connected to the control inputs of code-to-pulse duration converters which are equal in number to the number of the windings of the synchronous machine, the outputs of the converters being connected to the pulse duration master inputs of a switching device whose pulse polarity master inputs are connected to the respective outputs of the permanent storage, the master inputs of the polarity of the control signal being united and adapted to receive a signal governing the polarity of the control signal, and the outputs being connected to the windings of the synchronous machine. This drive further comprising a master oscillator having its output connected to the input of a controlled frequency divider whose control input is adapted to receive a code of the modulus of the control signal and whose output is connected to the master inputs of pulse frequency of the code-to-pulse duration converters. A voltage source is connected to the switching device.
In the last-described rectifier electric drive variations of the output torque value still occur at reversing and on account of the absence of means for compensating for pulsation and drift of the supply voltage. They are, however, smaller than in the previously described rectifier drive, owing to the permanence of the frequency or repetition rates of the pulses supplying the windings. Furthermore, on account of the finiteness of the impedance of the voltage source, the flatness of the mechanical characteristics of the electric drive is not adequately high.